diff --git a/spec/ruby/core/thread/thread_variable_get_spec.rb b/spec/ruby/core/thread/thread_variable_get_spec.rb
index 67017771fd..e8e03e3d18 100644
--- a/spec/ruby/core/thread/thread_variable_get_spec.rb
+++ b/spec/ruby/core/thread/thread_variable_get_spec.rb
@@ -41,13 +41,20 @@ describe "Thread#thread_variable_get" do
     @t.thread_variable_get(:a).should be_nil
   end
 
-  it "does not raise a TypeError if the key is neither Symbol nor String, nor responds to #to_str" do
-    @t.thread_variable_get(123).should be_nil
+  it "raises a TypeError if the key is neither Symbol nor String when thread variables are already set" do
+    @t.thread_variable_set(:a, 49)
+    -> { @t.thread_variable_get(123) }.should raise_error(TypeError, "123 is not a symbol")
   end
 
-  it "does not try to convert the key with #to_sym" do
-    key = mock('key')
-    key.should_not_receive(:to_sym)
-    @t.thread_variable_get(key).should be_nil
+  ruby_version_is '3.4' do
+    it "raises a TypeError if the key is neither Symbol nor String when no thread variables are set" do
+      -> { @t.thread_variable_get(123) }.should raise_error(TypeError, "123 is not a symbol")
+    end
+
+    it "raises a TypeError if the key is neither Symbol nor String without calling #to_sym" do
+      key = mock('key')
+      key.should_not_receive(:to_sym)
+      -> { @t.thread_variable_get(key) }.should raise_error(TypeError, "#{key.inspect} is not a symbol")
+    end
   end
 end
diff --git a/spec/ruby/core/thread/thread_variable_spec.rb b/spec/ruby/core/thread/thread_variable_spec.rb
index d64e6ec63d..465b985365 100644
--- a/spec/ruby/core/thread/thread_variable_spec.rb
+++ b/spec/ruby/core/thread/thread_variable_spec.rb
@@ -41,13 +41,20 @@ describe "Thread#thread_variable?" do
     @t.thread_variable?(:a).should be_false
   end
 
-  it "does not raise a TypeError if the key is neither Symbol nor String, nor responds to #to_str" do
-    @t.thread_variable?(123).should be_false
+  it "raises a TypeError if the key is neither Symbol nor String when thread variables are already set" do
+    @t.thread_variable_set(:a, 49)
+    -> { @t.thread_variable?(123) }.should raise_error(TypeError, "123 is not a symbol")
   end
 
-  it "does not try to convert the key with #to_sym" do
-    key = mock('key')
-    key.should_not_receive(:to_sym)
-    @t.thread_variable?(key).should be_false
+  ruby_version_is '3.4' do
+    it "raises a TypeError if the key is neither Symbol nor String when no thread variables are set" do
+      -> { @t.thread_variable?(123) }.should raise_error(TypeError, "123 is not a symbol")
+    end
+
+    it "raises a TypeError if the key is neither Symbol nor String without calling #to_sym" do
+      key = mock('key')
+      key.should_not_receive(:to_sym)
+      -> { @t.thread_variable?(key) }.should raise_error(TypeError, "#{key.inspect} is not a symbol")
+    end
   end
 end
diff --git a/thread.c b/thread.c
index 56f1399d41..45aa0565ca 100644
--- a/thread.c
+++ b/thread.c
@@ -3756,12 +3756,13 @@ static VALUE
 rb_thread_variable_get(VALUE thread, VALUE key)
 {
     VALUE locals;
+    VALUE symbol = rb_to_symbol(key);
 
     if (LIKELY(!THREAD_LOCAL_STORAGE_INITIALISED_P(thread))) {
         return Qnil;
     }
     locals = rb_thread_local_storage(thread);
-    return rb_hash_aref(locals, rb_to_symbol(key));
+    return rb_hash_aref(locals, symbol);
 }
 
 /*
@@ -3912,13 +3913,14 @@ static VALUE
 rb_thread_variable_p(VALUE thread, VALUE key)
 {
     VALUE locals;
+    VALUE symbol = rb_to_symbol(key);
 
     if (LIKELY(!THREAD_LOCAL_STORAGE_INITIALISED_P(thread))) {
         return Qfalse;
     }
     locals = rb_thread_local_storage(thread);
 
-    return RBOOL(rb_hash_lookup(locals, rb_to_symbol(key)) != Qnil);
+    return RBOOL(rb_hash_lookup(locals, symbol) != Qnil);
 }
 
 /*